A developed power supply system is always present on modern real estate objects. Despite the high operational reliability, abnormal situations sometimes occur in this system for various reasons. The root cause of their danger lies in the high power transmitted over the network. When selected in a limited area, defined, for example, by isolation violations, this is leads to a sharp increase in temperature, which in severe cases is accompanied by the occurrence fire.
Appointment of a fire-prevention RCD
To protect against potentially dangerous for users leakage currents, an RCD is installed in the electrical network.
When building power wiring:
- it is divided into separate directions-rays, each of which is equipped with its own individual protective element;
- in addition, one common group RCD is installed in the same switchboard, to the output of which individual ones are connected in parallel.
This structure, the diagram of which is shown in Figure 1, is convenient for the ability to disconnect individual segments, and its 2-stage design contributes to more reliable protection.
The presence of a fire-resistant RCD provides protection:
- input feeder against fire due to degradation of insulation;
- those wiring lines in which there is no dedicated differential machine.
The presence of an additional stage of protection makes the operation of the wiring safer.
Structural differences of a fire-prevention RCD and recommendations for its implementation
From the point of view of their constructive form factor and internal design, fireproof RCDs are similar to conventional ones, as shown in Figure 2, and differ from them:
- increased to 100 or 300 mA threshold for leakage current, i.e. at least three times higher in comparison with the RCD of direct protection;
- referring to the speed of the S-type with a response time of the order of 250 ms.
The need to choose just such parameters is determined by a good compromise between the required normal operation sensitivity and good protection against false alarms in real networks. In addition, it allows the achievement of the property of selectivity, i.e. tripping the RCD one by one in the direction from bottom to top. The latter is important from the point of view of the simplicity of finding the fault location.
In the case of a branched electrical network, a 3-stage circuit is sometimes built.
As the installation site for the RCD under consideration, the storey switchboard of an apartment building or its analogue in a cottage is usually chosen. An example is shown in Figure 3.
Electromechanical and electronic fire protection RCDs are available for sale. All other things being equal, it is recommended to use these devices in an electromechanical design, fully retaining their functionality even in a situation of power loss.